The Third Generation Partnership Project (3GPP) has developed the standard for a system, newly named as EPS (Evolved Packet System), in which a long term evolution (LTE) program provides improved spectral efficiency, reduced latency, and improvement in use of radio resources. The EPS allows users to experience high data-rate and abundant applications and services at lower cost than before. To obtain connectivity to the EPS, users have to get user equipment (UE) based on LTE. From the recent market trends, it has been considered that the UE would support multiple different radio technologies. For example, all of cellular phones have at least a wireless cellular interface for accessing a mobile cellular network. Among these cellular phones, the number of cellular phones having an IEEE 802.11 wireless interface capable of accessing a wireless local area network (WLAN) has been increasing.
FIG. 1 shows a system described in the Third Generation Partnership Project (3GPP). In this system, UE 0100 obtains connectivity to a global communication network 013 through a wireless cellular interface (IF 01000). The IF 01000 communicates with eNB 0101 (Enhanced Node B) as a base station in connection with a 3GPP radio access network 010. The 3GPP radio access network may be, but not limited to, a UMTS Radio Access Network (UTRAN) or an E-UTRAN (Evolved UTRAN). The eNB 0101 has a signaling path (S0101) provided with a Mobility Management Entity (MME 0102). The eNB 0101 performs radio resource management and admission control on the UE 0100.
Further, the eNB 0101 performs header compression, encryption, and reliable packet delivery. The MME 0102 performs idle-mode mobility signaling for the UE 0100. This includes tracking and paging for the UE 0100. Further, the MME 0102 executes bearer activation/deactivation processes for the UE 0100. For this technique, a bearer is an information transmission path of defined capacity, delay or bit error rate. Through a signaling path S0101, the eNB 0101 can carry control information, such as the location of the UE 0100, or a request message from the UE 0100. When transmitting data to the global communication network 013, the UE 0100 needs to establish a data path. The MME 0102 uses a signaling path (S0103) provided with a serving gateway (S-GW 0103) to set a data communication path (S0102) toward the IF 01000 of the UE 0100. The signaling path S0102 between the eNB 0101 and the S-GW 0103 enables the transmission of data packets from the UE 0100.
The S-GW 0103 assists in rouging user data packets. Further, the S-GW 0103 serves as a mobility anchor point for the user plane during handover between different access systems. A packet data network gateway (PDN-GW 0104) provides, to the UE 0100, the connectivity to an external packet data network. The PDN-GW 0104 also has the ability to route user data packets based on a filtering rule (routing rule) described by the UE 0100. The S-GW 0103 sets up a data path for the UE 0100 using a signaling path S0104. When the UE 0100 transmits a data packet from the IF 01000 to a correspondent node (CN 0106), the data packet passes through the signaling paths S0102, S0104, S0105, and S0106. In this system, the correspondent node (CN 0106) is an entity performing end-to-end data communication with the UE 0100. As an example, data traffic between the UE 0100 and the CN 0106 is a flow of teleconference calls including video packet streams and voice packet streams. The CN 0106 uses the data path S0106 to communicate with the global communication network 013. When UMTS is used, eNB is replaced with RNC/BSC, MME is replaced with SGSN, and PGW is replaced with GGSN.
Further, the UE 0100 can establish another connection to the global communication network 013 through the wireless interface (IF 01001) for the wireless local area network (WLAN). The IF 01001 may be, but not limited to, any non-3GPP wireless interface, such as an IEEE 802.11 interface, a WiMAX interface, or a cdma 2000 High Rate Packet Data (HRPD) interface. The IF 01001 communicates with an ePDG 0105 (Evolved Packet Data Gateway) in connection with a non-3GPP radio access network 011. The non-3GPP radio access network may be, but not limited to, WLAN, WiMAX, or HRPD. The ePDG 0105 sets up a signaling path S0107 to the PDN-GW 0104 so that the UE 0100 can transmit data to the CN 0106.
In this system, a protocol for the UE 0100 to connect to the PDN-GW 0104 simultaneously on the 3GPP radio access network and on the non-3GPP radio access network uses an extended function of dual stack mobile IPv6 (DSMIPv6) (See Non-Patent Document 1). Using a binding identifier (BID), the UE 0100 can uniquely identify both the IF 01000 connection and the IF 01001 connection to the PDN-GW 0104. The BID is carried on a binding update (BU) message from the UE 0100 to the PDN-GW 0104. The BU message is a periodic update message sent from the UE 0100 to the PDN-GW 0104 to inform the PDN-GW 0104 that the UE 0100 remains connected. Therefore, the PDN-GW 0104 operating as a home agent (HA) for the UE 0100 has two possible packet forwarding paths to the UE 0100. A first path is signaling data paths S0104 and S0102. A second path is a signaling data path S0107.
When roaming around in a communication network, the UE 0100 as a mobile terminal can connect the IF 01000 to a different eNB. Referring again to FIG. 1, the IF 01000 can leave the communication area of the 3GPP radio access network 010 to move into the communication area of a 3GPP radio access network 012. To this end, the IF 01000 is associated with an eNB 0107. In the 3GPP, many discussions have been held on the idea that a telecommunications carrier performs selective IP traffic offload (SIPTO) (See Non-Patent Document 2). SIPTO as a function discussed in a framework called Release 10 in the 3GPP enables the UE to offload to another PDN-GW based on the location of the UE. This PDN-GW has the capability to transmit data packets from the UE directly to the global communication network 013 without passing through a core network of a cellular communications operator (offload path or local breakout path). Such an offload scheme enables the cellular communications operator to make effective use of precious radio resources thereof.
Referring again to FIG. 1, a local PDN-GW (L-GW 0108) has the functions as an S-GW and a PDN-GW. The L-GW 0108 is connected to the eNB 0107 through a signaling path S0110. The function of the L-GW 0108 enables the transmission of data packets from the UE 0100 to the global communication network 013 through a signaling path S0108. This is called breakout in the 3GPP. In this state, the data packets from the UE are transmitted promptly to the global communication network 013 without passing through the core network of the telecommunications carrier. This can lead to the saving of resources of the telecommunications carrier in the core network. It is considered that the offload from the UE to the PDN-GW is triggered by the MME 0102. In FIG. 1, it is assumed that the L-GW 0108 has both functions as the S-GW and the PDN-GW, but another entity having the function as the S-GW may exist between the L-GW 0108 and the eNB 0107. Further, the L-GW 0108 may be a normal PDN-GW existing in the core network. In this case, the advantage of offload from the PDN-GW 0104 is that the processing load on the PDN-GW 0104 or the S-GW 0103 can be dispersed.
The MME 0102 is the best candidate because it can recognize the location of the UE 0100 necessary to decide on the best timing of triggering the offload. When detecting that the UE 0100 can be offloaded, the MME 0102 sends a signal of such an intention to the eNB 0107 through a signaling path S0109. The reason for the MME 0102 to trigger such offload is that the cellular communications operator detects that the consumption of the radio resources reaches a constraining point and thinks of allocating part of the resources of the UE to a PDN-GW capable of transmitting data packets from the UE to the global communication network 013 without going through many networks of the cellular communications operator to release the resources, but it is not limited thereto. Similarly, the MME 0102 signals the L-GW 0108 to establish a PDN connection for the UE 0100 through S0111.
There are some existing methods of offloading the UE to another PDN-GW. On the 3GPP radio access network, the MME 0102 can try to disconnect the PDN connection to the IF 01000 of the UE 0100. The MME 0102 can perform a detach procedure or bearer deactivation procedure described in Non-Patent Document 3. The MME 0102 requests the IF 01000 to reestablish the connection to the PDN-GW 0104 through a message from the MME 0102 to the IF 01000. When the IF 01000 executes the PDN connectivity request, the MME 0102 selects the L-GW 0108. Thus, the MME 0102 offloads the IF 01000 from the PDN-GW 0104 to the L-GW 0108. Similarly, the MME 0102 negotiates the termination of the data signaling paths (S0102 and S0104) to the IF 01000.
On the non-3GPP radio access network, the PDN-GW 0104 can try to offload the IF 01001 of the UE 0100 to the L-GW 0108. The PDN-GW 0104 can perform a home agent (HA) relocation procedure described in Non-Patent Document 4. The IF 01001 receives, from the PDN-GW 0104, a message indicative of the L-GW 0108 as a new HA for the UE 0100. The IF 01001 tries to disconnect the connection to the PDN-GW 0104 and establish a connection to the L-GW 0108. Thus, the PDN-GW 0104 offloads the IF 01001 from the PDN-GW 0104 to the L-GW 0108.
It is apparent from the description so far that separate entities manage the mobility of the interfaces of the UE on the access networks in the 3GPP system. The MME monitors the location of the UE in connection with the mobility of the cellular interface of the UE on the 3GPP radio access network. The PDN-GW monitors the location of the UE in connection with the mobility of the WLAN interface of the UE on the non-3GPP radio access network. In the 3GPP system, since the MME and the PDN-GW do not work with each other, a problem may arise when the MME triggers the offload of the UE to another PDN-GW. Referring to FIG. 1, it is assumed that the 3GPP radio access signaling data paths (S0102 and S0104) and the non-3GPP radio access signaling data path (S0107) start congesting due to a lot of signaling thereon. At this point, the MME 0102 triggers the offload of the IF 01000 from the PDN-GW 0104 to the L-GW 0108 to reduce congestion on the signaling data paths (S0102 and S0104). Offload to an uncongested signaling paths (S0110 and S0108) removes a packet delivery delay or jitter of the current session (i.e., teleconference calls) of the UE 0100.
However, the MME 0102 is unaware that the UE 0100 has the IF 01001 connected to the PDN-GW 0104 on the non-3GPP radio access network 011. When the MME 0102 signals the S-GW 0103 to terminate (drop) the signaling path S0102 to the IF 01000, there is no indication that this termination is caused by the offload of the UE 0100 to another PDN-GW by means of the MME 0102. The lack of this indication is the same as in the S-GW 0103. The S-GW 0103 does not inform the PDN-GW 0104 that the termination of the data signaling path S0104 is caused by the offload of the UE 0100 to another PDN-GW by means of the MME 0102. Therefore, the PDN-GW 0104 managing the mobility of the IF 01001 of the UE 0100 will not trigger the HA relocation procedure for moving the HA being connected to the IF 01001 to the L-GW 0108. Since the signaling path S0107 exists, the PDN-GW 0104 can continue to forward data packets from the UE 0100, causing the UE 0100 to continue the congested paths. For ease of understanding, this problem will be described with the following example.
When the UE 0100 and the CN 0106 are in connection with each other to establish communication with a teleconference system, it is assumed that this communication consists of components of a voice session and a video session. The teleconference communication is destined to a UE home address (HoA) serving as an anchoring address of the UE 0100. Since the CN 0106 transmits data packets of the teleconference communication to the HoA, the CN 0106 does not recognize the mobility of the UE. The UE 0100 can get data packets transmitted from the CN 0106 regardless of the roaming destination of the UE 0100. If either of paths between the PDN-GW 0104 and the UE 0100 is disconnected, the PDN-GW 0104 will use the other path to forward the data packets to the UE 0100.
Since voice needs a certain quality of service (QoS), the UE 0100 has a filter rule to send voice packets toward the IF 01000 on a 3GPP radio access network. For video packets that do not require the QoS, the UE 0100 has a filter rule to send video packets toward the IF 01001 on a non-3GPP radio access network. When the IF 0100 is offloaded to the L-GW 0108, the signaling paths (S0102 and S0104) between the PDN-GW 0104 and the IF 01000 are disconnected by the UE 0100. However, the signaling path S0107 remains, and therefore, the PDN-GW 0104 can still forward both the voice and video packets to the IF 01001. Since the QoS for the voice packets is not provided to the signaling path S0107, some slight delay and jitter occur in the teleconference communication. For example, both parties concerned feel that the relationship between conversation and images is disrupted. The quality of user's call is degraded, and in some cases, this leads to an income loss for the cellular communications operator.
Patent Document 1 describes a method for UE to notify a MME of the type of radio access to the destination when the UE has connected to a network of a cellular communications operator. For example, when the UE intends to establish connections to both the 3GPP radio access network and the non-3GPP radio access network, the UE notifies the MME of its intention. Therefore, this problem is solved by this conventional technique to notify the MME that the UE has a connection on the non-3GPP radio access network. This information can assume that the MME knows the time of notifying the PDN-GW when deciding to offload the UE to another PDN-GW. However, this conventional technique does not give a detailed description on an indication between the MME and the PDN-GW at the time when the UE has been offloaded.
Patent Document 2 teaches a process capable of determining whether a data session is congested on one of multiple interfaces of UE. If so, the UE can forward the data session to another uncongested interface. This process includes a comparison between the maximum processing capacity value for a specific session on a specific interface and a processing capacity value for all sessions on the same interface. As a result of the comparison, when the processing capacity value for the data session is smaller than the sum of the processing capacity values for all the sessions on the same interface, the data session is forwarded to another interface. Thus, this conventional technique causes the UE always to monitor and compare all data sessions on various interfaces of the UE to solve this problem. However, it seems that always monitoring and comparing all the data sessions on various interfaces of the UE increases the requirements to be processed in the UE. Thus, it can be said that this conventional technique solves this problem by the possibility of additional processing in the UE capable of being allocated for any another purpose.
Based on Non-Patent Document 1, since the UE 0100 has a connection to the PDN-GW through the non-3GPP radio access network, the PDN-GW 0104 sends the MME 0102 a notification of a request not to change the database of a home subscription server (HSS). Upon receipt of this notification, the MME 0102 can estimate that the UE 0100 is connected to the PDN-GW 0104 through the non-3GPP radio access network. However, since the MME 0102 controls only the 3GPP radio connection of the UE 0100 so far, the MME 0102 has no means for requesting the UE 0100 to terminate the non-3GPP radio access connection to the PDN-GW 0104. Therefore, the signaling path S0107 to the PDN-GW 0104 remains present.